How to understand Plutonium enrichment in the graph

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Discussion Overview

The discussion revolves around understanding the relationship between plutonium enrichment and critical diameter as presented in a specific graph. Participants explore the implications of varying levels of Pu-240 and Pu-239 in terms of their fissionability and neutron absorption properties.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant presents a graph indicating that different enrichments of plutonium correspond to varying critical diameters, questioning why lower enrichment results in a smaller diameter.
  • Another participant suggests that Pu-240 is not easily fissionable and may absorb neutrons, proposing that a lower amount of Pu-240 leads to a smaller critical diameter.
  • A subsequent post seeks clarification on whether the enrichment percentages refer specifically to Pu-240, implying that 5% wt indicates 5% Pu-240 and 95% Pu-239.
  • Further discussion confirms the assumption that the enrichment numbers refer to Pu-240, but there is uncertainty about the composition of the remaining plutonium.

Areas of Agreement / Disagreement

Participants express differing views on the implications of plutonium enrichment and its components, with some agreeing on the role of Pu-240 while others remain uncertain about the overall composition of the plutonium.

Contextual Notes

There is ambiguity regarding the definitions of enrichment percentages and the exact composition of plutonium when one isotope is specified. The discussion does not resolve these uncertainties.

Who May Find This Useful

Individuals interested in nuclear physics, particularly those studying plutonium isotopes and their properties in criticality safety contexts.

Neutroniclad
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http://ncsp.llnl.gov/ARH-600/files/pdfs/III.A.4-2.pdf
For a certain fixed density (let's say 1g/cm3) different enrichment corresponds with different cylinder diameter
20% wt 12.0in
15% wt 11.2in
10% wt 10.4in
5% wt 9.6in
0% wt 8.4in
Why the decrease of enrichment result in a smaller critical diameter?
 
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I think Pu-240 isn't fissionable or not as easily while it may absorb neutrons. Hence the less Pu-240, the less the critical diameter
 
DrDu said:
I think Pu-240 isn't fissionable or not as easily while it may absorb neutrons. Hence the less Pu-240, the less the critical diameter
Thank you for your opinion.
So you mean the number here refers to the enrichment of Pu-240? i.e. 5%wt means 5% Pu-240 with 95% Pu-239.
If so, does 0%wt refers to 100% Pu-239? Or is there something else in the plutonium?
 
Neutroniclad said:
So you mean the number here refers to the enrichment of Pu-240?
Yes, it says so. But I can't judge from only the graph that the rest is Pu-239. However, I would suppose so.
 
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